1. Field of the Invention
The present invention relates to an ethylene vinyl acetate (EVA) based compound film having a thickness of 0.01 to 2 mm, preferably, 0.1 to 1.0 mm, rather than a conventional form in sheet shape having a thickness of 2.5 to 3.0 mm or a palletized shape having a thickness of 3.0 to 4.0 mm and a height of 4 to 5.0 mm. The present invention also relates to shoe components including an insole, midsole, unitsole of midsole and outsole, an upper, and upper components. Shoe components produced through the manufacturing method using the film of the present invention have a wide variety of colors and outer appearances. In addition, it is possible to design and produce shoe components with their own colors and mechanical properties including density, hardness, abrasion, resiliency, compression set and stiffness/flexibility in consideration of function of each shoe component.
2. Description of the Related Art
In a conventional method, shoe components including an upper component, midsole, outsole, insole and a unitsole of midsole and outsole are produced by using a foamed article or articles obtained from the processes performed after completion of the foaming process, wherein the article is made of an EVA copolymer having a shape of a hard plate sheet, pellet or a chip having a thickness of 2.5 mm or higher, and a surface non-uniformity which can be easily discriminated by touch or sight. Shoe components are produced by a compression molding or injection molding process (primary process) and a compression re-molding process (secondary process). The above-described conventional method will be explained in detail with reference to FIG. 1, as follows. In FIG. 1, S stands for step.
Primary Process: Foam Molding Process
(1) Compression Molding Process
A1) A material is selected, measured and weighed in consideration of the relations of the volume, physical property and expansion ratio or the mold cavity related to them. The pieces of the material obtained by cutting a sheet stock or weighing palletized EVA copolymer compound. (step SA1).
B1) The material is put into the cavity of an open/shut type compression molding mold which is proportionally miniatured shape of the shoe component by certain percentages in consideration of the relations between the volume of the crosslinked blown EVA form and expansion ratio of the compound. (step SB1).
The molding mold is pressed and heated for a predetermined time period (step SC1).
The molding die is released and rapidly open (step SD1), when it is possible to form a cell structure from the gas including N2, CO2, CO, NH3 generated during the process of decomposition of the foaming agent during the step SC1, and the material in the molding die has a low viscosity permitting a foaming process.
The volume of the crosslinked blown EVA form may differ in accordance with the expansion ratio and the shape of the internal part of the molding mold, that is, volume of the cavity, design of mix proportion of EVA compound and purposes of the blown EVA form. The volume of the form is 120 to 140% of the final shoe component when the form is used in a secondary compression molding process. The volume of the form is determined by the shape of the cavity of the molding mold which is miniatured in consideration of the volume of the form according to the formability required for the secondary compression re-molding process and changes of physical properties occurring before and after the secondary compression re-molding process, and the expansion ratio of the material.
In cases where the primary compression molded body is shaped into an EVA sponge plate, cut and surface/shape grinded, bonded to the other material and used as a final shoe component, or in cases where the primary compression molded body is used as a final shoe component without performing a secondary compression re-molding process, the form has a size and physical properties which are not stable.
E1) Therefore, the form is cooled for a predetermined time period in the space with no pressure (step SE1). This step is for stabilization of the structure and shape of the individual cell in the form, and volume and physical properties of the form in consideration of the design reference size of the component or product.
The form obtained through the step SE1 is used as a shoe component after performing the processes including a trimming, cutting and bonding, or used as an intermediate form for a compression re-molding process, a secondary process. The intermediate form has a density 60 to 70% or a volume 120 to 140% of the final form, in consideration of the compression re-molding process.
In steps SC1 and SD1, a compression molding machine has a molding part which is selectively maintained at a vacuum state so as to achieve improved flowability and formability of the material. This is to overcome drawbacks of the conventional compression molding method, including a non-uniformity of flow and low formability of the material.
(2) Injection Molding Process
An injection molding process mainly uses a pellet type EVA copolymer, as described with reference to FIG. 1.
A2) A pellet type material is measured and weighed in consideration of the volume of the mold cavity and expansion ratio of the palletized compound. (step SA2).
B2) The material is molten in an injecting machine and injected into the cavity of the injection molding mold along the channel of the molding mold (step SB2).
The subsequent processes include steps SC2 and SE3, explained below. However, in some cases, the material is molten in the injecting machine, injected into the cavity of the warm injection mold that being heated at a very lower temperature, cooled so as to avoid premature reaction of the blowing agent dispersed in the injected compound. and released (step SB12). Subsequently, steps SB1 to SE1 of the compression molding process can be performed for the resultant material.
C2) The molding mold is pressed and heated for a predetermined time period (step SC2).
D2) The molding mold is released and rapidly open (step SD2).
E2) The form is cooled for a predetermined time period in the space with no pressure (step SE2).
Detailed descriptions on steps SD2 and SE2 are identical with the description on steps SD1 and SE1 of the compression molding process.
(1) Heat/Cold Mold Compression Re-molding Process
This process is for producing a final form from the intermediate form obtained from the compression or injection molding process described above.
F1) The intermediate form which has volume 120 to 140% of the final form is compulsorily put into the cavity of the compression molding mold (step SF1).
The cavity of the molding mold is designed to correspond to the size and shape of the final form, and the molding mold is generally made of an aluminum material having a high thermal conductivity.
G1) The molding mold is shut and applied with a predetermined temperature and pressure (step SG1).
H1) The molding mold is cooled and released (step SH1), thereby obtaining a final form.
The heat/cold mold compression re-molding process including steps SF1 to SH1 is for a component with a large thickness, like a midsole, outsole, unitsole and an insole. The heat/cold mold compression re-molding process is widely known as a representative technique of the secondary re-molding process performed in association with the compression molding process and the injection molding process.
The upper component or insole which can be formed of a form having a small thickness and low accuracy of molding, is produced through a cold mold compression re-molding process.
(2) Cold Mold Compression Re-molding Process
F2) The intermediate form is heated by an external heating source, and loaded into the cavity of an open type cold molding die (step SF2).
G2) The material is cold shaped by applying a predetermined pressure through the core of the upper part of the molding mold. (step SG2)
H2) The pressure is released and the cold molded form is released from the molding mold so as to be used as a final form (step SH2).
The EVA crosslinked blown EVA form produced through the first and second processes, by using a hard sheet or pellet, has drawbacks as follows.
First, it is conventional knowledge obtained through bio-mechanical studies and experiments, that shoe sole components for each part of the wearer's foot need differentiated functions. For example, it is desirable to form the lateral side of the rear foot of the wearer from the material having a low hardness or hard material for supporting an arch part, and the fore foot part from the material having a cushioning capability.
In a conventional method, each part of EVA forms compose a sole unit of shoe having different physical properties is independently formed and bonded with each other after formation so as to satisfy the above-described need for differentiated functions.
As shown in FIG. 2, forms A and B are produced through steps S1A to S5A and S1B to S5B, and assembled and bonded in a step S6AB. Alternatively, foam molded forms obtained from the compression or foam molding steps S3A and S3B are assembled with each other in a step S3AB, and compression re-molded in a step S4AB to as to thereby obtain a final form. However, the above-described conventional method has drawbacks with respect to complex manufacturing procedures, high manufacturing costs, and degradation of outer appearance and function including defects in adhesion.
Second, in a conventional method, each shoe part is manufactured independently, assembled and bonded with each other, and painted or printed independently so as to obtain a variety of colors and designs. This causes restrictions in design and deterioration of durability and productivity, while increasing costs.
Third, each shoe part has different physical properties and is manufactured through independent forming and bonding procedures so as to achieve improved abrasion resistance, cushioning, stability and wearing comfort.
Fourth, The shapes of the material used in a conventional method do not allow for a wide range of selection, making it impossible to accomplish a wide variety of functions from each portion of a sole component foamed by crosslinked blown EVA form. That is, it is hard to obtain a final form with light weight, high abrasion resistance and regional multi density design within a single form through the primary foam molding process or the secondary compression re-molding process.
Fifth, use of a conventional sheet or pellet type EVA compound causes increases in manufacturing procedures and costs, preventing diversification of physical properties and design of each part of the form.
Sixth, use of a conventional sheet type EVA compound causes non-uniformity of surface and high variation in thickness, for example 2.5 to 3.0 mm. Therefore, when the sole component is obtained through the primary foam molding process or secondary compression re-molding process, it is hard to obtain quality reproducibility for a mass production. The shape of the sheet type material has to be controlled in X, Y and Z axes, and it is extremely difficult to accurately control the shape in every axes or boundaries of each EVA forms used in different color or physical property within a single form of the component during the foam by either compression or injection molding includes compression re-molding process, to fit the standard of design.
Seventh, a conventional method where the primary compression molded body is shaped into an EVA sponge plate, cut and surface/shape grinded, bonded to the other material and used as a final shoe component, produces significant amount of wastes during cutting and grinding processes.